The required capacity of backhaul networks grows exponentially in recent years. While copper or fiber optic based wired systems can provide data throughput of 10 Gbps or more, the microwave radio channel throughput of traditional frequency bands between 6 and 42 GHz is currently 500 Mbps or less. In order to increase the data throughput of wireless communication, link aggregation schemes are used where two or more microwave radios are connected in parallel as shown in FIG. 1A.
FIG. 1A is an exemplary illustration of an all outdoor radios link aggregation system 100A with a star-like wired connection. High-speed data traffic (which is typically in Ethernet format but could be in any other digital format) is connected to a first radio unit 101A. The digital data interface module 101A-1 in the first radio unit 101A splits the incoming data into two or more data streams. Each data stream has a data rate that is equal to or less than the throughput of a single microwave radio. One data stream is transmitted by the first radio unit 101A. The other data streams are connected to the other radios such as a second radio unit 102A and a third radio unit 103A in the link aggregation system using high-speed digital cables (which are typically Ethernet cable but could be any other digital cable). Different radio units transmit data streams using different carrier frequencies. On the local side, the output Radio Frequency (RF) signal of each transceiver (101A-3, 102A-3, and 103A-3) is transmitted to an antenna coupling unit (ACU) 104, which combines them together and transmits the combined data streams to an antenna and subsequently into the air. The ACU 104 is a passive device that allows multiple transmitters to be connected to the same antenna. On the remote side, the received RF signal is delivered to a corresponding ACU that is configured to transmit the received RF signal to multiple receivers. Note that the equipment on the remote side has the same configuration as the one shown in FIG. 1A except that the ACUs are located on the left side and the digital data interfaces are on the right side. Different radio units are tuned on different carrier frequencies to receive one data stream. The digital data streams from some radios are connected to the digital data interface of the first radio, which combines them together to reconstruct the original data traffic and sends the data traffic to the user's equipment. In this configuration, the first radio unit 101A (i.e., the master radio) has multiple weatherproof connectors on its enclosure, each weatherproof connector used for connecting to another radio unit in the link aggregation system. This increases the size of the all outdoor radio enclosure. Because the other radio units are usually of the same type as the first radio unit 101A, all the other radio units will have extra outdoor connectors that are not used at the same time. Further, the installation and maintenance of multiple outdoor-rated high-speed cables between the radio units in the link aggregation system is difficult and expensive.
FIG. 1B illustrates an alternative, currently used approach of having multiple radio daisy-chained. In this daisy-chain approach, each all outdoor radio unit splits the incoming data into two data streams: one data stream to be transmitted by the radio unit itself and having a data rate equal to or less than the throughput of the radio unit, and the second data stream, which contains the remaining data, is forwarded to the next radio unit in the chain. Using this daisy-chain approach, each all outdoor radio unit only needs one extra connector. But this daisy-chain approach causes more latency because the overall latency is determined by the longest path in the link aggregation system.
In addition, wireless communication in current radio backhaul networks may be affected and deteriorated for various reasons, for example, multipath interference, hardware failure, selective path fading etc. In order to protect the wireless communication against these factors, microwave radio units may often be deployed in a one plus one (1+1) protection mode such as hot standby configuration, space diversity configuration, frequency diversity configuration, or hybrid diversity configuration. The radio units that participate in the protection configuration need to exchange data and signaling information to ensure proper operation.
Currently, all outdoor radios protection system may employ a high speed digital wired connection to exchange information between the radio units. The transmission speed of the digital wired connection may be up to 1 Gigabits per second (Gbps) in full duplex mode.
FIG. 1C illustrates an exemplary illustration of an all outdoor radios protection system 100B using a wired connection in related art. As illustrated in FIG. 1C, a first radio unit 101B and a second radio unit 102B are deployed in the protection configuration. A first protection interface 108B of the first radio unit 101B and a second protection interface 115B of the second radio unit 102B are connected by an outdoor digital cable with a transmission speed up to 1 Gbps in full duplex mode.
Finally, an XPIC application is often employed in current radio backhaul networks to improve the capacity of a radio frequency (RF) channel, which effectively doubles the capacity of an RF channel by allowing two microwave radio units to operate on the same frequency. One radio unit uses the vertical polarization while the other radio unit uses the horizontal polarization. Demodulator in each radio unit of the XPIC application receives, respectively, intermediate frequency (IF) signals from a local receiver and from the receiver of the other radio unit operating an opposite polarization. Demodulator uses the IF signal from the other radio to cancel the interference from the opposite polarization in the IF signal from the local receiver caused by limited antenna cross polarization discrimination.
FIG. 1D is an exemplary illustration of an all outdoor radios system implemented with an XPIC application using a wired connection in related art. As illustrated in FIG. 1D, a first radio unit 101C is configured to operate using the vertical polarization, and a second radio unit 102C is configured to operate using the horizontal polarization. A first demodulator 105C of the first radio unit 101C uses the IF signal 116C from the second radio unit 102C to cancel the interference from the horizontal polarization in the IF signal 115C from the first radio unit 101C.
When an XPIC application in combination with a protection system is employed in an all outdoor radios system, a total of six wired connections between the four radio units are required. FIG. 1E is an exemplary illustration of an all outdoor radios system equipped with a protection system and an XPIC application using a wired connection in related art. As illustrated in FIG. 1E, there are two wired XPIC interconnections 233C, 234 between a first radio unit 201C and a second radio unit 202C, two wired XPIC interconnections 237C, 238C between a third radio unit 203C and a fourth radio unit 204C, one wired protection interconnection 235C between the first radio unit 201C and the third radio unit 203C, and one wired protection interconnection 236C between the second radio unit 202C and the fourth radio unit 204C are required.
However, the wired XPIC and protection connections require both the weatherproof connectors on the enclosure of the all outdoor radio units and the outdoor rated digital cables. Due to the sizes of the antennas at certain frequency bands, the installation and maintenance of the XPIC pair of the all outdoor radio units may be difficult and expensive.